1. Field of the Invention
This invention relates generally to a sealing structure for a magnetic disk drive unit, and particularly to a structure of a packing assembly for sealing a magnetic disk drive unit.
2. Description of the Related Art
In recent years, the tendency has progressed towards a magnetic disk drive unit as a kind of an external memory unit for a computer made smaller in size and thinner in design. Also, there is a requirement for reduced consumption of electric power for such a magnetic disk drive unit. Moreover, an increased recording density of a hard disk is required in order to fulfil the requirement for larger capacity, and therefore, the number of hard disks to be loaded on the drive unit is increased.
In the magnetic disk drive unit for a computer, a constant start and stop (CSS) system is generally employed to regulate the working relationship between a magnetic head and a hard disk. In this system, during rotation of the hard disk, the magnetic head floats on the hard disk keeping a very small distance due to the balance of force between a floating force given by an air stream generated by the hard disk rotating at a high speed and a force of the spring arm pressing the magnetic head against the hard disk. When the rotation of the hard disk is stopped, the magnetic head moves to a contactable area on the hard disk and contacts the hard disk. During the stop of rotation of the hard disk, the head and the disk are in contact with each other.
As mentioned, since the magnetic head floats on the hard disk keeping a very small distance during rotation of the hard disk, head crash, etc. tend to occur caused by tiny dust or the like. To avoid this, the hard disks and the magnetic heads for writing and reading data to and from the hard disks are arranged in a sealed chamber defined within a disk enclosure (housing). The housing of the magnetic disk drive unit comprises a base housing, and a cover secured to the base housing by screws. For sealing the housing, an annular packing made of rubber material is interposed between the base housing and the cover and then the cover is secured to the base housing.
In a large-sized magnetic disk drive units of five inches or more, an annular groove is formed in the periphery of the base housing or in the periphery of the cover, the packing is inserted in this annular groove, and then the cover is secured to the base housing by screws. However, in a magnetic disk drive unit of 3.5 (three point five) or less inches, it is practically impossible to employ this mounting method of packing because it usually does not have a sufficient width for forming a groove in the mating (or abutting) surface of the base housing or the cover.
To overcome this problem, in the conventional magnetic disk drive units of 3.5 (three point five) or less inches, an annular packing made of soft rubber material is attached to the base housing by a pressure sensitive adhesive double coated tape and thereafter, the cover is screwed tight to the base housing. The reason why a pressure sensitive adhesive double coated tape is used for attaching the annular packing to the base housing is that the annular packing lacks rigidity due to its material of soft rubber, and therefore, if the pressure sensitive adhesive double coated tape is not used, the annular packing is difficult to attach to a predetermined location of the base housing in a stable fashion.
However, in the conventional method for using a pressure sensitive adhesive double coated tape to attach the annular packing to the base housing, the following problems occur during the time the magnetic disk drive unit is repaired. That is, it is necessary to remove the cover from the base housing when the magnetic disk drive unit is to be repaired. Since the annular packing is attached to the base housing and the cover by the pressure sensitive adhesive double coated tape, when the cover is removed from the base housing, residue of the pressure sensitive adhesive double coated tape adheres to the base housing and/or the cover. For reassembling the magnetic disk drive unit after the completion of repair, it is necessary to scrape off the residue of the tape before a new annular packing is attached. This takes time and labor to scrape off the residue.